166 AGRICULTURE. 



Mineral matters, e.g., phosphate of lime, sodium chlorid 



(common salt), etc. 



The Fuel Value of Food. — Heat and muscular power are 

 forms of force or energy. The energy is developed as 

 the food is consumed in the body. It is measured in the 

 laboratory by means of an apparatus called the calorimeter. 

 The unit commonly used is the calorie, the amount of heat 

 which would raise the temperature of a pound of water 

 four degrees Fahrenheit. 



Taking ordinary food materials as they come, the follow- 

 ing general estimate has been made for the average amount 

 of heat and energy in i pound of each of the classes of 

 nutrients: 



Calories. 



In I pound of protein i,86o 



In I pound of fats 4,220 



In I pound of carbohydrates 1,860 



In other words, when we compare the nutrients in re- 

 spect to their fuel values, their capacities for yielding heat 

 and mechanical power, a pound of protein of lean meat or 

 albumen of egg is just about equivalent to a pound of 

 sugar or starch, and a little over two pounds of either 

 would be required to equal a pound of the fat of meat or 

 butter or the body fat. 



Ways in which Food is Used in the Body. — Food supplies 

 the wants of the body in several ways. It either — 



Is used to form the tissues and fluids of the body; 



Is used to repair the wastes of tissues; 



Is stored in the body for future consumption; 



Is consumed as fuel, its potential energy being trans- 

 formed into heat or muscular energy, or other forms of 

 energy required by the body; or. 



In being consumed protects tissues or other food from 

 consumption. 



Uses of the Different Classes of Nutrients. — Protein forms 

 tissue (muscle, tendon, etc., and fat) and serves as fuel. 



Fats form fatty tissue (not muscle, etc.) and serve as fuel. 



Carbohvdrates are transformed into fat and serve as fuel. 



